Water deficit is considered the main abiotic stress that limits agricultural production worldwide. Brassinosteroids (BRs) are natural substances that play roles in plant tolerance against abiotic stresses, including water deficit. This research aims to determine whether BRs can mitigate the negative effects caused by water deficiency, revealing how BRs act and their possible contribution to increased tolerance of cowpea plants to water deficit. The experiment was a factorial design with the factors completely randomised, with two water conditions (control and water deficit) and three levels of brassinosteroids (0, 50 and 100 nM 24-epibrassinolide; EBR is an active BRs). Plants sprayed with 100 nM EBR under the water deficit presented significant increases in U PSII , q P and ETR compared with plants subjected to the water deficit without EBR. With respect to gas exchange, P N , E and g s exhibited significant reductions after water deficit, but application of 100 nM EBR caused increases in these variables of 96, 24 and 33%, respectively, compared to the water deficit ? 0 nM EBR treatment. To antioxidant enzymes, EBR resulted in increases in SOD, CAT, APX and POX, indicating that EBR acts on the antioxidant system, reducing cell damage. The water deficit caused significant reductions in Chl a, Chl b and total Chl, while plants sprayed with 100 nM EBR showed significant increases of 26, 58 and 33% in Chl a, Chl b and total Chl, respectively. This study revealed that EBR improves photosystem II efficiency, inducing increases in U PSII , q P and ETR. This substance also mitigated the negative effects on gas exchange and growth induced by the water deficit. Increases in SOD, CAT, APX and POX of plants treated with EBR indicate that this steroid clearly increased the tolerance to the water deficit, reducing reactive oxygen species, cell damage, and maintaining the photosynthetic pigments. Additionally, 100 nM EBR resulted in a better dose-response of cowpea plants exposed to the water deficit.

Drought frequently results in significant losses in agricultural systems, including the soybean yield. Brassinosteroids exhibit multiple actions on essential processes, including chlorophyll fluorescence and gas exchange. Considering that the electron transport rate (ETR) into photosystems can exercise interference on net photosynthetic rate (PN), this research aims to determine whether 24-epibrassinolide (EBR) affects electron transport and find out if there is any repercussion on photosynthesis in soybean plants affected by the water deficit. The experiment was performed using a randomized factorial design, with two water conditions (control and water deficit) and three EBR concentrations (0, 50, and 100 nM EBR). The water deficit reduced effective quantum yield of PSII photochemistry, ETR, PN, and water-use efficiency. However, the exogenous application of 100 nM EBR mitigated these negative effects, increasing these variables. EBR reduced the oxidant compounds (superoxide and hydrogen peroxide) and membrane damages (malondialdehyde and electrolyte leakage) in stressed plants. Our study proved that EBR increased ETR and PN in control and stressed plants, revealing that ETR had a strong relationship with PN. These results suggest that soybean plants with higher values of ETR are more efficient in relation to PN.Additional key words: chlorophyll fluorescence; drought; gas exchange; Glycine max; 24-epibrassinolide. transport rate; ETR/PN -ratio between the apparent electron-transport rate and net photosynthetic rate; EXC -relative energy excess at the PSII level; F0 -minimal fluorescence yield of the dark-adapted state; Fm -maximal fluorescence yield of the dark-adapted state; Fv -variable fluorescence; Fv/Fm -maximal quantum yield of PSII photochemistry; gs -stomatal conductance to water vapor; LDM -leaf dry matter; MDA -malondialdehyde; NPQ -nonphotochemical quenching; PEG -polyethylene glycol; PN -net photosynthetic rate; PN/Ci -instantaneous carboxylation efficiency; qP -photochemical quenching; RDM -root dry matter; ROS -reactive oxygen species; STM -stem dry matter; TDM -total dry matter; WUE -water-use efficiency; ΦPSII -effective quantum yield of PSII photochemistry. Acknowledgements: This research had financial support from Fundação Amazônia de Amparo a Estudos e Pesquisas (FAPESPA/Brazil), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil) and Universidade Federal Rural da Amazônia (UFRA/ Brazil) to AKS Lobato. While YC Pereira and WS Rodrigues were supported with scholarships from Programa de Educação Tutorial (PET/Brazil).

This study aims to explain the effects of silicon on chlorophyll and to measure gas exchange and carbohydrate levels in two Lycopersicon esculentum cultivars that are exposed to drought. The experimental design used in this study was a randomised combination of five different water and silicon conditions (control, water deficit + 0.00 μmol Si, water deficit + 0.25 μmol Si, water deficit + 1.00 μmol Si, and water deficit + 1.75 μmol Si) applied to the two cultivars (Super Marmante and Santa Cruz). Parameters measured were gas exchanges, chlorophylls, and total soluble carbohydrates. Silicon at concentrations of 0.25, 1.00, and 1.75 μmol induced a gradual increase in the total chlorophyll levels. A correlation analysis revealed a linear, positive interaction between the leaf water potential and the total chlorophyll (r = 0.71; P < 0.05). This study confirmed the hypothesis that silicon has a beneficial effect with regard to chlorophyll. Under water-deficient conditions, both cultivars showed an increase in chlorophyll a when treated with silicon in addition to changes in the total chlorophyll levels. These results were supported by the change in leaf water potential. In addition, a reduction of the effects of water restriction was also observed in the transpiration rate, the stomatal conductance and in the levels of total carbohydrates.

The objective of this study was to: first, evaluate the infection effects caused by Colletotrichum lindemuthianum pathogen (race 2047) on photosynthetic pigments and gas exchanges in Phaseolus vulgaris plants (cv. Mexico 222); and, second, determine infection effects on leaf pigments and their consequences on photosynthesis rate. A completely randomized design with a factorial scheme was used, combining two treatments (control and inoculated) and three evaluation periods (4th, 8th and 12th day). Carotenoid levels presented decreases of 28.3% and 35% during the 8th and 12th day after infection, when control and inoculated plants were compared. Correlation analysis demonstrated the direct relationship between carotenoids and photosynthesis rate (r 00.84). Total chlorophyll in infected plants had progressive reductions of 6.4%, 20.6% and 21.3% on the 4th, 8th and 12th day, respectively, when treated and untreated plants were compared. Total chlorophyll with photosynthesis (r 00.85) also revealed a significant and linear correlation. The photosynthetic rate in infected plants decreased by 22%, 49.9% and 77.3% on the 4th, 8th and 12th days after the inoculation, respectively. Anthracnose infection also induced negative effects concerning stomatal conductance, transpiration, photosynthesis and water use efficiency. Our results demonstrate that leaf pigment reduction as a result of pathogens was the main cause of lower gaseous exchanges in infected plants.

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